The present invention relates to reactivation of sorbents in furnace ash and more specifically for cooling, hydrating, and reactivating unutilized sulfur abatement sorbents in the furnace bottom ash.
During the combustion of fuels that contains sulfur compounds, such as coal, SO2, SO3 (collectively “SOx”) gasses are created. In addition to being green house gases, these gasses when released combine with water to create sulfuric acid (H2SO4) that is hazardous to the many ecosystems.
Crushed limestone is typically used to neutralize and eliminate the SOx gasses. In circulating fluidized bed (CFB) furnaces, which may be part of a boiler system, crushed limestone is added to the crushed fuel to neutralize the SOx gases during combustion. The combustion creates limestone products that consist of significant amounts of calcium oxide (CaO, unreacted lime) and calcium sulfate (CaSO4) and small amounts of calcium carbonate (CaCO3).
A significant amount of the limestone does not react with the SOx gasses, so typically about twice the stoichiometric amount of the limestone is used to realize satisfactory capture of the SOx gasses. The excess unreacted limestone is removed with the ash generated from the solid fuel combustion. There are two net discharge streams of ash from the CFB, i.e., bottom ash and flyash. Typically, the ash contains limestone product that consists of unutilized CaO. The bottom ash, limestone byproducts and unreacted lime are typically cooled and discarded as waste material.
One such device for cooling bottom ash is a Rotary Ash Cooler (RAC). A RAC is a rotating cylindrical conduit with an inlet at one end and an outlet at the opposite end. It has cooling pipes that run through the conduit wall. Hot bottom ash is received at the inlet and is moved by internal spiral fins to the outlet as the conduit rotates. By the time the bottom ash is at the outlet it has been cooled to the proper temperature. The bottom ash is then disposed with other wastes.
Conventional RAC devices have little or no sensing or adjustment devices. They are set by design and do not have a means of fine temperature control of the ash in the event of an unacceptable rise in temperature. This may occur for several reasons, e.g., with an unusual change in furnace operation, abnormal process conditions, varying fuel supply, or malfunction of other controls.
Excessive bottom ash temperatures may destroy ash-handling systems and may cause damage to the system. Excessive temperature may also create difficulty in transporting and disposing the ash in an environmentally acceptable manner.
Also, there is a significant amount of unused limestone is being wasted increasing operating costs and creating additional waste material that needs to be disposed.
Thus, there is a need for a method and device for more accurately monitoring bottom ash and for increasing the utilization of limestone by reusing unreacted CaO in the bottom ash.